1. Field of the Invention
This invention relates to a process for the production of a polyamide containing smaller amounts of gel-like substances, a polyamide which is produced by this process, and a film or sheet made of the polyamide.
2. Prior Art
As a general process for producing a high-molecular-weight polyamide using adipic acid as a dicarboxylic acid component, there are a process in which an aqueous solution of a salt of adipic acid and a diamine is formed and heated under increased pressure, and polycondensation is conducted while removing water formed, and a process in which adipic acid is heat-melted to form an adipic acid solution, and while adding dropwise a diamine to the adipic acid solution, polycondensation is conducted by removing water formed.
The above adipic acid as a starting material to produce the polyamide is industrially prepared by oxidizing cyclohexanol or a mixture (KA oil) of cyclohexanone and cyclohexanol with nitric acid.
Crude adipic acid obtained by nitric acid oxidation is purified by washing with water. The thus obtained adipic acid as a product contains 4 to 10 ppm by weight of free nitric acid. Said adipic acid sometimes contains other mineral acid used together with nitric acid in the nitric acid oxidation, e.g., hydrochloric acid, in a free form in an amount of 4 to 10 ppm based on the total amount of it and nitric acid.